Revert "drm/panel-edp: Allow querying the detected panel via sysfs"

This reverts commit 363c4c38.

Since the point of this attribute is for a test, this should be done
in debugfs, not sysfs. Let's revert and a new patch can be added later
doing it in debugfs.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220201092152.1.Ibc65ec6fa05017e9856ba9ef557310268429c3ce@changeid